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PUCET (Punjab) JEE Main 2023 Mixed — practice questions — page 2

Explore 95 free JEE Main 2023 Mixed questions in PUCET (Punjab) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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JEE Main 2023 Mixed questions and exercises with answers

Showing questions 31–60 of 95.

Rutherford's $\alpha$-particle scattering experiment used a thin foil of which metal?Read the answer and worked solution →For a hydrogen-like atom of nuclear charge $Z$, the radius of the $n$th Bohr orbit scales asRead the answer and worked solution →The energy of the $n$th Bohr orbit of a hydrogen-like atom isRead the answer and worked solution →The ratio of the radii of the third Bohr orbit of $He^+$ and the first Bohr orbit of $H$ isRead the answer and worked solution →The velocity of the electron in the $n$th Bohr orbit of a hydrogen-like atom is proportional toRead the answer and worked solution →The energy required to remove the electron from the first excited state ($n=2$) of $He^+$ isRead the answer and worked solution →Which series of the hydrogen spectrum lies entirely in the *visible* region?Read the answer and worked solution →Rydberg's formula for the wave number of a hydrogen spectral line isRead the answer and worked solution →The longest wavelength line in the Lyman series of hydrogen corresponds to the transitionRead the answer and worked solution →The de Broglie wavelength of a particle of mass $m$ and momentum $p$ isRead the answer and worked solution →The de Broglie wavelength of an electron in the $n$th Bohr orbit, in terms of the orbit radius $r_n$, isRead the answer and worked solution →An electron is accelerated through a potential difference of $100\,V$. Its de Broglie wavelength is approximatelyRead the answer and worked solution →Heisenberg's uncertainty principle relates the uncertainties in position and momentum asRead the answer and worked solution →The minimum uncertainty in the velocity of an electron whose position is known to within $\Delta x = 0.1\,nm$ is approximatelyRead the answer and worked solution →The principal quantum number $n$ can take valuesRead the answer and worked solution →For principal quantum number $n$, the orbital quantum number $l$ takes valuesRead the answer and worked solution →For orbital quantum number $l$, the magnetic quantum number $m_l$ takes valuesRead the answer and worked solution →How many orbitals are present in the $n = 3$ shell?Read the answer and worked solution →The maximum number of electrons in the subshell with $n = 4, l = 2$ isRead the answer and worked solution →Which set of quantum numbers $(n, l, m_l, m_s)$ is **NOT** allowed?Read the answer and worked solution →Hund's rule applies during the filling ofRead the answer and worked solution →The Aufbau principle dictates that orbitals fill in order of increasingRead the answer and worked solution →Which of the following orbital shapes is dumbbell-shaped along an axis?Read the answer and worked solution →How many *angular* nodes does a $3d$ orbital have?Read the answer and worked solution →The number of *radial* nodes in a $4s$ orbital isRead the answer and worked solution →The ionisation energy of hydrogen in its ground state isRead the answer and worked solution →For $He^+$, the ionisation energy from its ground state isRead the answer and worked solution →Which transition in the hydrogen atom emits the largest amount of energy?Read the answer and worked solution →Which of the following experimental phenomena could **NOT** be explained by classical EM wave theory?Read the answer and worked solution →The Bohr model failed to explainRead the answer and worked solution →

Worked practice questions

Rutherford's $\alpha$-particle scattering experiment used a thin foil of which metal?

  1. Copper
  2. Gold
  3. Aluminium
  4. Silver
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Correct answer: B. Gold

Gold is highly malleable — it can be hammered into a foil only a few atoms thick, which is what the experiment needed to keep most $\alpha$-particles passing through.

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For a hydrogen-like atom of nuclear charge $Z$, the radius of the $n$th Bohr orbit scales as

  1. $r_n \propto nZ$
  2. $r_n \propto n^2/Z$
  3. $r_n \propto Z/n^2$
  4. $r_n \propto n/Z^2$
Show answer and solution

Correct answer: B. $r_n \propto n^2/Z$

$r_n = (0.529\,Å)\,n^2/Z$. **So radius grows as $n^2$ but shrinks as $Z$ — explaining why He$^+$ has a smaller $n=1$ orbit than H.**

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The energy of the $n$th Bohr orbit of a hydrogen-like atom is

  1. $E_n = -13.6\,n^2/Z^2\,eV$
  2. $E_n = -13.6\,Z^2/n^2\,eV$
  3. $E_n = -13.6\,Z/n\,eV$
  4. $E_n = +13.6\,Z/n\,eV$
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Correct answer: B. $E_n = -13.6\,Z^2/n^2\,eV$

$E_n = -13.6 \times Z^2/n^2\,eV$. Negative because the electron is *bound* $n=1, Z=1$ gives the ground-state H energy of $-13.6\,eV$.

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